Average current mode controlled converter having a buck mode, a boost mode, and a partial four-switch mode
An average current-mode controlled converter has a buck mode, a boost mode, and a four-switch mode. In one example, the converter operates in one of the three modes, depending on the difference between the converter output voltage VOUT and the converter input voltage VIN. Whether the four-switch mode is a full-time four-switch mode or a partial four-switch mode is user programmable. The novel converter can also be programmed to operate in other ways. For example, the converter can be programmed so that there is no intervening four-switch mode, but rather the converter operates either in a buck or a boost mode depending on VOUT-VIN. The converter can also be programmed so that the converter always operates in a conventional full-time four-switch mode. In one embodiment, the converter is programmed by setting an offset between two internally generated ramp signals and by setting associated limiting and inverting circuits.
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The present disclosure relates generally to converters that are operable in a buck mode, a four-switch mode, and a boost mode, depending on a difference between an output voltage VOUT and an input voltage VIN.
BACKGROUNDA DC-to-DC switched mode power supply may employ a circuit involving an inductor and four switches. A first of the switches (S1) is coupled between a source of a rough DC voltage VIN and a first terminal of the inductor. A second of the switches (S2) is coupled between the first terminal of the inductor and a ground node. A third of the switches (S3) is coupled between a second terminal of the inductor and the ground node. A fourth of the switches (S4) is coupled between the second terminal of the inductor and a load. If the switches are made to switch in a first fashion, then the power supply operates as a “buck converter” in that it converts a higher input voltage VIN into a smaller DC output voltage VOUT that is supplied to the load. If the switches are made to switch in a second fashion, then the power supply operates as a “boost converter” in that it converts a lower input voltage VIN into a larger DC output voltage VOUT on the load.
In some applications, it is useful to switch the switches of the circuit such that the circuit operates as a buck converter at some times and operates as a boost converter at other times. Consider, for example, an application in which a battery is used to supply a circuit with a fixed DC supply voltage. When the battery is fully charged, the DC voltage from the battery is larger than the DC voltage required by the circuit. The intervening power supply therefore operates as a buck converter, receives the higher input battery voltage, and outputs the lower DC voltage required by the circuit. As the battery discharges, however, the DC voltage output by the battery decreases. At a certain point, the DC voltage output by the battery is lower than the DC voltage required by the circuit. The intervening power supply then is made to operate as a boost converter. The boost converter receives the lower DC voltage from the battery and outputs the higher required DC voltage to the circuit. The intervening power supply may be referred to as a “buck-boost” converter. There are many known topologies for buck-boost converters.
Although the circuits of
A flexible and adaptable average current mode controlled DC-to-DC converter is programmable to operate in a buck mode, a boost mode, and a four-switch mode. The mode in which the converter operates is determined by the difference between the converter output voltage VOUT and the converter input voltage VIN. In one operational example, if VOUT-VIN is a relatively large negative value then the converter operates in a pure buck mode, whereas if VOUT-VIN is approximately zero then the converter operates in a four-switch mode, whereas if VOUT-VIN is a relatively large positive value then the converter operates in a pure boost mode. Whether the four-switch mode is a full-time four-switch mode or a partial four-switch mode can be quickly and easily programmed by the user by setting digital programming bits. In one example, the digital programming bits are serially loaded and stored into the converter and are utilized in a ramp generator portion of the converter.
The novel converter can also be user programmed to operate in a selectable one of other ways. For example, the converter can be user programmed so that there is no intervening four-switch mode between the buck mode and the boost mode, but rather the converter operates either in buck or boost mode depending on VOUT-VIN. The converter can also be user programmed so that the converter always operates in a conventional full-time four-switch mode regardless of the magnitude of VOUT-VIN such that the converter has no conventional buck or boost modes.
In one embodiment, the converter is user programmed by setting a DC voltage offset between two internally generated ramp signals and by setting an associated error voltage limiting circuit and an associated inverting circuit. The DC voltage offset is actually changed within the converter as a selectable function of VOUT-VIN. A ramp generator sets the DC voltage offset depending on the current magnitude of VOUT-VIN according to the selected function. The ramp generator also sets the associated error voltage limiting circuit and the associated inverting circuit so that the overall converter operates properly in the mode selected by the user.
In one example, the novel converter is realized as a standard tile. The tile is of an architecture that facilitates the rapid integration of the tile into a larger Chip Scale Package (CSP) integrated circuit involving other tiles. The offset voltage to VOUT-VIN function is set by loading programming data into the CSP integrated circuit via a master tile, and then transferring the programming data from the master tile and into the buck/four-switch/boost tile. The programming data may be stored in the buck/four-switch/boost tile in non-volatile memory.
Other structures and methods are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.
The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.
Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.
Integrating voltage error amplifier 8 receives the output voltage VOUT on output node 18, voltage divides VOUT using a voltage divider involving resistors 19 and 20 thereby generating a centertap voltage VCENT proportional to VOUT. A first operational transconductance amplifier (OTA1) 21 compares VCENT to a reference voltage VREF and outputs a current signal whose magnitude is indicative of the voltage difference between VCENT and VREF. The current signal output by OTA1 21 is frequency compensated by block 22. Block 22 may, for example, be an analog low pass filter involving a capacitor and a resistor. The resulting voltage signal VE1 is a first error signal that is output onto node 23. VE1 is indicative of an error between VOUT and a desired value of VOUT.
A second operational transconductance amplifier (OTA2) 24 of integrating current error amplifier 9 compares a current sense signal VCS on node 25 to the first error voltage VE1 on node 23. Voltage VCS is indicative of the magnitude of current IL flowing in inductor 4. VCS may, for example, be generated using an inductor DCR current sense circuit involving a RC or an RCR circuit coupled across the terminals 16 and 17 of inductor 4.
The resulting current error signal on node 26 is filtered by an RC circuit involving-resistor 27 and capacitor 28. The filtered signal passes through a programmable voltage limiter (PVL) 29 and is output onto node 30 as a second error voltage signal VE2. The overall integrating current error amplifier circuit 9 therefore integrates, over several switching cycles, the difference between the required current (as determined by VE1) and the current sensed (as determined by VCS). VE2 sets the average current flowing through inductor 4 in each switching cycle.
The voltage to which PVL 29 limits VE2 is set by ramp generator 31. For example, in a first setting PVL 29 allows VE2 to range from zero volts to a maximum of 1.0 volts, whereas in a second setting PVL 29 allows VE2 to range from zero volts to a maximum of 1.5 volts. Ramp generator 31 controls PVL 29 in accordance with the selected offset voltage to VOUT-VIN function, as described in further detail below.
Pulse width modulation circuit 10 includes ramp generator 31. Ramp generator 31 receives a multi-bit digital programming data value (PG) via terminals 15 and conductors 15A. Ramp generator 31 also receives the input voltage VIN and the output voltage VOUT. Ramp generator 31 uses the programming data value, the input voltage VIN and the output voltage VOUT to generate a first ramp voltage signal RAMP1 and a second ramp voltage signal RAMP2 such that a programmable DC voltage offset voltage exists between the two ramp signals. A first comparator with hysteresis 32 compares the second error voltage VE2 with the first ramp signal RAMP1. The signal output by first comparator 32 is selectably inverted by inverter 34 and multiplexer 35. Whether the signal is inverted or is not inverted is determined by ramp generator 31. The resulting signal as output by multiplexer 35 is a first pulse width modulation signal PWM1. PWM1 controls the switching of switches A and B as illustrated. If PWM1 is high, then switch A is ON and switch B is OFF. Otherwise, if PWM1 is low, then switch A is OFF and switch B is ON. A second comparator with hysteresis 33 compares the second error voltage VE2 with the second ramp signal RAMP2 to output a second pulse width modulation signal PWM2. PWM2 controls the switching of switches D and C as illustrated. If PWM2 is high, then switch D is ON and switch C is OFF. Otherwise, if PWM2 is low, then switch D is OFF and switch C is ON. In one novel aspect, ramp generator 31 changes the offset voltage between the two ramp signals RAMP1 and RAMP2 as a programmable function of VIN and VOUT.
If, however, VOUT-VIN exceeds −1.0 volts, then as indicated in
As indicated in
If, however, VOUT-VIN exceeds +1.0 volts, then as indicated in
In one novel aspect, the converter 1 of
As indicated in
As indicated in
In one novel aspect, the four-switch mode can be made to be a selectable one of the full-time four-switch mode and the partial four-switch mode by appropriate programming of ramp generator 31. In both cases, current mode control is used. In the prior art voltage mode control circuit of
In addition to the offset voltage versus (VOUT-VIN) functions of
In
Although the novel average current mode controlled converter having a buck mode, a boost mode, and a partial four-switch mode is explained above in connection with an embodiment in which the pulse width modulation circuit 10 operates by generating two ramp signals, other circuits for generating the desired PWM1 and PWM2 signals can be employed. In one example, a single ramp signal is generated and a programmable offset voltage is added to the second error voltage VE2 as it is supplied to one of the comparators 32 and 33. Other offset voltage to VOUT-VIN functions can be employed other than, or in addition to, the particular exemplary functions set forth above. The waveform diagrams set forth above are simplifications. For more accurate waveforms, the actual circuit to be realized can be simulated using a circuit simulator (for example, SPICE) that outputs waveform diagrams. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.
Claims
1. A method comprising:
- (a) generating a first error signal that is indicative of an error between an output voltage (VOUT) of a DC-to-DC converter and a reference voltage, wherein the DC-to-DC converter has a pure buck mode, a partial four-switch mode, a full-time four-switch mode and a pure boost mode;
- (b) generating a current sense signal indicative of a current in an inductor of the DC-to-DC converter;
- (c) comparing the current sense signal to the first error signal to generate a second error signal;
- (d) using the second error signal to generate a first switch control signal and a second switch control signal, wherein the first switch control signal determines a first switching cycle current flowing through one of the first and second switches, wherein the second switch control signal determines a second switching cycle current flowing through one of the third and fourth switches, wherein if an input voltage (VIN) of the DC-to-DC converter is substantially greater than VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in the pure buck mode, and wherein if VIN is substantially smaller than VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in the pure boost mode; and
- (e) programming the DC-to-DC converter to operate in the full-time four-switch mode rather than the partial four-switch mode when the input voltage VIN and the output voltage VOUT are approximately equal.
2. The method of claim 1, wherein when the DC-to-DC converter operates in a partial four-switch mode there is an amount of time in which the second and third switches are OFF and the first and fourth switches are ON.
3. An average current mode controlled DC-to-DC converter having a pure buck mode, a partial four-switch mode, and a pure boost mode, wherein the DC-to-DC converter comprises:
- an inductor;
- a first switch coupled between an input voltage node and a first terminal of the inductor;
- a second switch coupled between the first terminal of the inductor and a ground node;
- a third switch coupled between a second terminal of the inductor and the ground node;
- a fourth switch coupled between an output node and the second terminal of the inductor, wherein during the partial four-switch mode the first switch and the fourth switch are ON during a time that both the second switch and the third switch are OFF;
- an integrating voltage error amplifier that compares an output voltage (VOUT) of the DC-to-DC converter to a reference voltage and that outputs a first error signal;
- an integrating current error amplifier that compares a current sense signal to the first error signal and that outputs a second error signal, wherein the current sense signal is indicative of a magnitude of a current flowing through the inductor, wherein the second error signal determines an average current of at least one of the first, second, third and fourth switches; and
- a pulse width modulation circuit that includes a programmable ramp generator, wherein the pulse width modulation circuit uses an output from the programmable ramp generator and the second error signal to generate switch control signals that determine the current flowing through the first, second, third and fourth switches.
4. A method comprising:
- (a) generating a first error signal that is indicative of an error between an output voltage (VOUT) of a DC-to-DC converter and a reference voltage;
- (b) generating a current sense signal indicative of a current in an inductor of the DC-to-DC converter;
- (c) using the current sense signal and the first error signal to generate a second error signal; and
- (d) using the second error signal to generate a first switch control signal and a second switch control signal, wherein the first switch control signal determines a first switching cycle current flowing through one of the first and second switches, wherein the second switch control signal determines a second switching cycle current flowing through one of the third and fourth switches, wherein if an input voltage (VIN) of the DC-to-DC converter is substantially greater than VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in a pure buck mode, wherein if VIN is approximately equal to VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in a partial four-switch mode, wherein if VIN is substantially smaller than VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in a pure boost mode, and wherein (d) involves:
- generating a first ramp signal;
- generating a second ramp signal; and
- changing an offset between the first and second ramp signals as a function of VIN and VOUT.
5. An average current mode controlled DC-to-DC converter having a pure buck mode, a partial four-switch mode, and a pure boost mode, wherein the DC-to-DC converter comprises:
- an inductor;
- a first switch coupled between an input voltage node and a first terminal of the inductor;
- a second switch coupled between the first terminal of the inductor and a ground node;
- a third switch coupled between a second terminal of the inductor and the ground node;
- a fourth switch coupled between an output node and the second terminal of the inductor, wherein during the partial four-switch mode the first switch and the fourth switch are ON during a time that both the second switch and the third switch are OFF;
- an integrating voltage error amplifier that compares an output voltage (VOUT) of the DC-to-DC converter to a reference voltage and that outputs a first error signal;
- an integrating current error amplifier that receives a current sense signal and the first error signal and that outputs a second error signal, wherein the current sense signal is indicative of a magnitude of a current flowing through the inductor, wherein the second error signal determines an average current of at least one of the first, second, third and fourth switches; and
- a pulse width modulation circuit that receives the second error signal and generates a first switch control signal and a second switch control signal, wherein the first switch control signal determines a first switching cycle current flowing through one of the first and second switches, wherein the second switch control signal determines a second switching cycle current flowing through one of the third and fourth switches, and wherein the pulse width modulation circuit comprises a ramp generator circuit that outputs a first ramp signal and a second ramp signal, wherein the second ramp signal is offset from the first ramp signal by an offset voltage, and wherein the ramp generator changes the offset voltage as a function of an input voltage (VIN) of the DC-to-DC converter and the output voltage (VOUT) of the DC-to-DC converter.
6. An average current mode controlled DC-to-DC converter having a pure buck mode, a partial four-switch mode, and a pure boost mode, wherein the DC-to-DC converter comprises:
- an inductor;
- a first switch coupled between an input voltage node and a first terminal of the inductor;
- a second switch coupled between the first terminal of the inductor and a ground node;
- a third switch coupled between a second terminal of the inductor and the ground node;
- a fourth switch coupled between an output node and the second terminal of the inductor, wherein during the partial four-switch mode the first switch and the fourth switch are ON during a time that both the second switch and the third switch are OFF;
- an integrating voltage error amplifier that compares an output voltage (VOUT) of the DC-to-DC converter to a reference voltage and that outputs a first error signal;
- an integrating current error amplifier that receives a current sense signal and the first error signal and that outputs a second error signal, wherein the current sense signal is indicative of a magnitude of a current flowing through the inductor, wherein the second error signal determines an average current of at least one of the first, second, third and fourth switches; and
- a pulse width modulation circuit that receives the second error signal and generates a first switch control signal and a second switch control signal, wherein the first switch control signal determines a first switching cycle current flowing through one of the first and second switches, wherein the second switch control signal determines a second switching cycle current flowing through one of the third and fourth switches, and wherein the pulse width modulation circuit comprises a ramp generator circuit that outputs a first ramp signal and a second ramp signal, wherein the second ramp signal is offset from the first ramp signal by an offset voltage, and wherein the offset voltage has a constant value.
7. The average current mode controlled DC-to-DC converter of claim 6, wherein the pulse width modulation circuit comprises:
- a first comparator that compares the first ramp signal to the second error signal; and
- a second comparator that compares the second ramp signal to the second error signal.
8. An average current mode controlled DC-to-DC converter having a pure buck mode, a partial four-switch mode, a full-time four-switch mode and a pure boost mode, wherein the DC-to-DC converter operates in the pure buck mode if an input voltage (VIN) of the DC-to-DC converter is substantially higher than an output voltage (VOUT) of the DC-to-DC converter, wherein the DC-to-DC converter operates in a selectable one of the partial four-switch mode and the full-time four-switch mode if VIN is approximately equal to VOUT, and wherein the DC-to-DC converter operates in the pure boost mode if VIN is substantially lower than VOUT.
9. An average current mode controlled DC-to-DC converter having a pure buck mode, a partial four-switch mode, a full-time four-switch mode and a pure boost mode, wherein the DC-to-DC converter comprises:
- an inductor;
- a first switch coupled between an input voltage node and a first terminal of the inductor;
- a second switch coupled between the first terminal of the inductor and a ground node;
- a third switch coupled between a second terminal of the inductor and the ground node; and
- a fourth switch coupled between an output node and the second terminal of the inductor, wherein during the partial four-switch mode the first switch and the fourth switch are ON during a time that both the second switch and the third switch are OFF, and wherein all four switches switch substantially simultaneously during the full-time four-switch mode.
10. The average current mode controlled DC-to-DC converter of claim 9, wherein the DC-to-DC converter has a full-time four-switch mode, wherein during the full-time four-switch mode there is substantially no amount of time that both the second and third switches are OFF.
11. The average current mode controlled DC-to-DC converter of claim 9, wherein during the full-time four-switch mode there is no amount of time during which both (a) the first switch and the fourth switch are simultaneously on and (b) the second switch and the third switch are simultaneously off.
12. The average current mode controlled DC-to-DC converter of claim 9, wherein during the full-time four-switch mode both (a) the first switch and the fourth switch are simultaneously on and (b) the second switch and the third switch are simultaneously off for no more than 1% of each switching cycle of the inductor.
13. A DC-to-DC converter comprising:
- a first switch coupled between an input voltage node and a first inductor node, wherein an input voltage (VIN) is present on the input voltage node;
- a second switch coupled between the first inductor node and a ground node;
- a third switch coupled between a second inductor node and the ground node;
- a fourth switch coupled between an output node and the second inductor node;
- an integrating voltage error amplifier that compares an output voltage (VOUT) of the DC-to-DC converter to a reference voltage and that outputs a first error signal;
- an integrating current error amplifier that compares a current sense signal to the first error signal and that outputs a second error signal, wherein the current sense signal is indicative of a magnitude of an inductor current; and
- a pulse width modulation circuit that includes a programmable ramp generator, wherein the pulse width modulation circuit uses an output from the programmable ramp generator and the second error signal to generate switch control signals that determine when the first, second, third and fourth switches switch, and wherein the DC-to-DC converter is operable in a partial four-switch mode in which the first and fourth switches are ON during a time that the second and third switches are OFF, wherein the DC-to-DC converter is also operable in a pure buck mode and in a pure boost mode.
14. The DC-to-DC converter of claim 13, wherein the DC-to-DC converter is programmable such that the DC-to-DC converter does not operate in any four-switch mode but rather operates in the pure buck mode or the pure boost mode depending on a magnitude of VOUT-VIN.
15. The DC-to-DC converter of claim 13, wherein the DC-to-DC converter is programmable such that the DC-to-DC converter operates in a full-time four-switch mode rather than the partial four-switch mode when the input voltage VIN and the output voltage VOUT are approximately equal, wherein the DC-to-DC converter operates in the pure buck mode if VIN is substantially greater than VOUT, and wherein the DC-to-DC converter operates in the pure boost mode if VIN is substantially smaller than VOUT.
16. A DC-to-DC converter comprising:
- a first switch coupled between an input voltage node and a first inductor node, wherein an input voltage (VIN) is present on the input voltage node;
- a second switch coupled between the first inductor node and a ground node;
- a third switch coupled between a second inductor node and the ground node;
- a fourth switch coupled between an output node and the second inductor node;
- an integrating voltage error amplifier that compares an output voltage (VOUT) of the DC-to-DC converter to a reference voltage and that outputs a first error signal;
- an integrating current error amplifier that receives a current sense signal and the first error signal and that outputs a second error signal, wherein the current sense signal is indicative of a magnitude of an inductor current; and
- a pulse width modulation circuit that receives the second error signal and generates a first switch control signal and a second switch control signal, wherein the first switch control signal determines when the first and second switches switch, wherein the second switch control signal determines when the third and fourth switches switch, wherein the DC-to-DC converter is operable in a partial four-switch mode in which the first and fourth switches are ON during a time that the second and third switches are OFF, wherein the DC-to-DC converter is also operable in a pure buck mode and in a pure boost mode, wherein the pulse width modulation circuit includes a ramp generator circuit that outputs a ramp signal, and wherein the pulse width modulation circuit changes the ramp signal as a function of the input voltage VIN and the output voltage VOUT.
17. A method comprising:
- (a) generating a first error signal that is indicative of an error between an output voltage (VOUT) of a DC-to-DC converter and a reference voltage;
- (b) generating a current sense signal indicative of a current in an inductor of the DC-to-DC converter;
- (c) using the current sense signal and the first error signal to generate a second error signal; and
- (d) using the second error signal to generate a first switch control signal and a second switch control signal, wherein the first switch control signal determines a first switching cycle current flowing through one of the first and second switches, wherein the second switch control signal determines a second switching cycle current flowing through one of the third and fourth switches, wherein if an input voltage (VIN) of the DC-to-DC converter is substantially greater than VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in a pure buck mode, wherein if VIN is approximately equal to VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in a partial four-switch mode, wherein if VIN is substantially smaller than VOUT then the first, second, third and fourth switches are controlled in (d) such that the DC-to-DC converter operates in a pure boost mode, and wherein (d) involves:
- generating a ramp signal; and
- changing the ramp signal as a function of VIN and VOUT.
18. An integrated circuit comprising:
- a first switch coupled between an input voltage node and a first inductor node;
- a second switch coupled between the first inductor node and a ground node;
- a third switch coupled between a second inductor node and the ground node;
- a fourth switch coupled between an output voltage node and the second inductor node; and
- means for determining a voltage difference between an output voltage VOUT on the output voltage node and an input voltage VIN on the input voltage node by comparing the output voltage VOUT to the input voltage VIN and for controlling the first, second, third and fourth switches such that first, second, third and fourth switches are operable as part of an average current mode controlled DC-to-DC converter having a pure buck mode, a partial four-switch mode, and a pure boost mode, wherein whether the average current mode controlled DC-to-DC converter is operating in the pure buck mode, the partial four-switch mode, or the pure boost mode depends upon the voltage difference between the ouput voltage VOUT and the input voltage VIN.
19. The integrated circuit of claim 18, wherein the means is also for controlling the first, second, third and fourth switches such that first, second, third and fourth switches are operable as part of an average current mode controlled DC-to-DC converter that has no pure buck mode, and no pure boost mode, but rather operates in a four-switch mode regardless of a voltage difference between VOUT and VIN.
20. The integrated circuit of claim 18, wherein the means is also for controlling the first, second, third and fourth switches such that first, second, third and fourth switches are operable as part of an average current mode controlled DC-to-DC converter having a pure buck mode, a full-time four-switch mode, and a pure boost mode, wherein whether the average current mode controlled DC-to-DC converter is operating in the pure buck mode, the full-time four-switch mode, or the pure boost mode depends upon a voltage difference between VOUT and VIN.
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Type: Grant
Filed: Aug 22, 2008
Date of Patent: Mar 27, 2012
Patent Publication Number: 20100045254
Assignee: Active-Semi, Inc. (British Virgin Islands (VG))
Inventor: Matthew A. Grant (Palo Alto, CA)
Primary Examiner: Jeffrey Sterrett
Attorney: Imperium Patent Works
Application Number: 12/229,538
International Classification: G05F 1/59 (20060101);